AFTER THE WAR: THE MILITARY; ALLIES TO RETAIN LARGER IRAQ FORCE AS STRIFE PERSISTS

Faced with armed resistance that has killed four American soldiers this week, allied military commanders now plan to keep a larger force in Iraq than had been anticipated and to send war-hardened units to trouble spots outside Baghdad, senior American officials said today.

Instead of sending home the Third Infantry Division, which led the charge on Baghdad, American officials are developing plans that call for most of its troops to extend their stay and be used to quell unrest and extend American control.

Allied officials said that about 160,000 American and British troops were in Iraq and that most were likely to stay until security improves and other nations eased the burden by contributing troops.

Tens of thousands of logistics and transportation troops in Kuwait also support the Iraq deployment. As a result, the total number of allied forces involved directly and indirectly in securing Iraq is 200,000 or more, American military officials estimate.

A new assessment of allied troop requirements is being prepared by the Army's V Corps, which assumes command next month of allied forces in Iraq. The review is not expected to be completed for several days but one American officer said, ''The planning is looking at moving elements of the Third Division to hot spots outside of Baghdad.''

The size of the American force used to enforce the peace in Iraq has important implications for the Pentagon debate over how to restructure the military and how many Army forces are needed in future. Gen. Eric K. Shinseki, the Army chief of staff, predicted in February that hundreds of thousands of American troops would be needed to secure Iraq after a war.

That estimate was criticized by Defense Secretary Donald H. Rumsfeld and Deputy Secretary Paul D. Wolfowitz as a gross overestimate of what might be needed. ''The idea that it would take several hundred thousand U.S. forces I think is far off the mark,'' said Mr. Rumsfeld, who has shown interest in cutting the size of the Army.

Defense Department civilians generally avoided providing their own estimate in public but some suggested that a force of about 100,000 American troops might be sufficient at the start and that the figure could quickly taper off. They asserted that the Iraqis would hail the Americans as liberators, that Iraq had little history of ethnic strife and that nations like France, which opposed the war, would assist in reconstruction.

With the new assessment, one possibility is that a substantial portion of the Third Infantry Division will be deployed to Falluja, 35 miles west of Baghdad, according to military officials. Fifteen Iraqis were killed and dozens were wounded in clashes with American soldiers last month, and two more Iraqis died after attacking American soldiers last week. On Tuesday, two American soldiers were killed and nine were wounded there after they came under fire at a checkpoint.

Some of the fire directed at the Americans came from nearby buildings, including a mosque, American officials said.

Other units from the division -- an infantry battalion or perhaps a cavalry squadron -- may be sent north of Baghdad to reinforce the Fourth Infantry Division, which is charged with policing a huge swath of territory from Tikrit to Kirkuk to the Iranian border. A brigade is also likely to be kept in Baghdad to serve as a reserve force to back up the First Armored Division, officials said.

The Third Infantry Division led the attack to Baghdad, and its M-1 tanks were the first to roll into the city. The division has been charged with providing security in Baghdad and many of its soldiers had expected to leave after the First Armored Division assumed responsibility for security in the Iraqi capital this week.

Some of the Third Infantry Division units have been in the Persian Gulf region for nine months. The idea of extending the deployment has come as a shock to many of the division's soldiers, who say they have done more than their share by leading the charge to Baghdad. But senior officials in the division hope that a new mission will raise morale, which has sagged as the division's deployment has been extended.

In addition to delaying the withdrawal of the Third Infantry Division some additional forces -- engineers and intelligence units -- may be sent from the United States.

The initial plan developed by American military commanders for reducing deployments in Iraq was consist with optimistic Defense Department assumptions. American military officials outlined a plan a month ago that would have reduced the American troop presence to less than two divisions by September, a force of 70,000 or substantially less, including logistical support.

That plan assumed that security would improve considerably and that troops from other nations would arrive to ease the burden on American and British forces. But continued attacks by remnants of Saddam Hussein's forces and paramilitary units, violence by criminal groups, slow progress toward rebuilding the Iraqi police and security forces and the vast amount of territory to be secured have led American commanders to rethink their plans about the pace of the reductions.

''You adapt to conditions,'' an American officer said.

One factor is geography. American commanders assert that security in Baghdad has been improving. The Army First Armored Division, which is fresh and has experience in peacekeeping operations in the Balkans, recently arrived in Iraq, as did the rest of the Second Armored Cavalry Regiment. In addition, some 4,000 military police officers have also been sent to the capital.

Even as American troops step up their efforts in Baghdad, however, they have become more concerned about areas outside the city. The Third Armored Cavalry Regiment is charged with securing a huge area that stretches from Baghdad to the Jordanian and Syrian borders. One soldier was killed in an ambush near the Syrian border this week.

The Fourth Infantry Division, which is deployed north of Baghdad, also has responsibility for the area from Tikrit to Kirkuk and toward the Iranian border. Its soldiers also monitor the Mujahedeen Khalq, the Iranian resistance movement that has turned over its heavy weapons and stays in designated areas northeast of Baghdad. There have been a series of attacks by rocket propelled grenades and a recent drive-by shooting directed against the Fourth Infantry Division. Citing the large area it has to cover, the division has asked the V Corps to send more forces up north, officials said.

Regarding the Third Infantry Division, the division's First and Second Brigades are the units expected to stay on. The division's Third Brigade is expected to be the first of the division's brigades to return home. That brigade went to Kuwait, returned to the United States and then was sent back to Kuwait for the war. As a result, it has been deployed abroad for 12 of the last 15 months.

Currently, there are 145,000 American Army and Marine forces in Iraq. With the inclusion of British forces, the number of allied troops is about 160,000. About 90,000 American troops are in Kuwait. Some are en route to the United States from Iraq, but many are supporting the American deployment in Iraq.